State officials say the situation in Paulsboro “is stable” and are waiting to determine exactly what failed on a rail bridge crossing that was recently revamped following a 2009 train derailment.

John Burzichelli, a state assemblyman and Paulsboro’s former long-time mayor, said Friday that the National Transportation Safety Board will investigate the exact cause of the derailment that sent at least 18 people to the hospital for precautionary measures after they reported breathing problems.

The 84-car train was carrying vinyl chloride, a highly toxic and flammable material, when it tumbled into the Mantua Creek and began leaking the hazardous chemical, Burzichelli said. Emergency crews were able to stabilize the situation and are continuing to monitor the air at the accident site and in the surrounding area.

“[We’re] not certain if the bridge failed or the track failed, but obviously something failed,” said Burzichelli, adding that the rail crossing, known as a “swing bridge,” is an older bridge but was recently revamped.

“The bridge had an extensive rebuild, but something failed,” he said.

At least 22 people were affected by the chemical spill but there were no reports of serious injury so far, said Burzichelli, who is serving as a spokesman for the town.

“The response locally was good,” he said, adding that the next “window of incident” is when the cars are pulled from the creek.